Modals of speculation about the past

1. When can we use them?
We use the modal verbs must, may, might,
could or can’t to speculate about events in
the past.

2. LESS CERTAIN: may, might and could
MORE CERTAIN: must
Certain that the statement is false: can’t,
couldn’t

4. We use must to make deductions when we
are almost sure or more certain.

5. For past deductions we use
must + have + past participle:
He’d been working for 10 hours
when I saw him. He must have
been very tired.

6. We use can’t to make negative
deductions from evidence.
.

7. For past we use
can’t + have + past participle:
He can’t have failed the exam. He’s a very
good student!

8. We use may/ might / could to make
speculations (i.e. when there is no evidence).

9. We use may / might / could + have + past
participle for past:
He may/might/ could have phoned while
you were out. The answer phone was
switched off.

10. Deduction
must have and can't have + past participle
The plane ________ ________ run out of fuel.
It _________ ________ blown up in mid-air.

11. Speculation
could/may/might have + past participle
What could ________ happened to them?
They could _____ _____ up on a desert island.
Earhart and Noonan may _____ _____ US spies.
Aliens _______ _______ abducted them.

12. We use ________ ________ when we are sure
something happened.
We use ________ ________ when we are sure
something didn't happen.
We use _______ _______ ______ ______ to talk
about what possibly happened.